The present invention relates generally to an automatic picture aspect ratio conversion for a television receiver. In particular, the present invention relates to an automatic aspect ratio (AR) detecting method and AR compensating apparatus for a television receiver having a double window function whereby the ARs of two different video sources are detected, and if the detected ARs are different from each other, they are respectively converted into those most suitable for being displayed as double window pictures on a screen of the television receiver.
A conventional AR converting apparatus for a television receiver, as shown in FIG. 1, includes a sync separating section 10 for separating a sync signal from an input luminance signal Y, a pulse generating section 20 for generating a pulse signal for pedestal clamping utilizing the sync signal outputted from the sync separating section 10, a luminance detecting section 30 for detecting existence/nonexistence of the luminance signal in accordance with the pedestal clamping pulse signal generated from the pulse-generating section 20, a latch 40 for temporarily storing data for existence/nonexistence of the luminance signal outputted from the luminance detecting section 30, a dedicated microcomputer 50 for aspect ratio conversion (ARC) for receiving the data for existence/nonexistence of the luminance signal from the latch 40 and detecting the width of a horizontal scanning line during a vertical sync signal period to detect the AR of an input video signal, and a main microcomputer 60 for compensating for deflection data in accordance with the AR detected by the ARC-dedicated microcomputer 50.
Meanwhile, a typical television receiver having a double window function, as shown in FIG. 3, includes main-channel and sub-channel decoders 101 and 102 for decoding an input main-channel composite video signal MCVBS and sub-channel composite video signal SCVBS, respectively, a controller 103 for clamping, filtering, and data-processing the composite video signals decoded by the main-channel and sub-channel decoders 101 and 102, a video random access memory (RAM) 104 for storing and outputting data processed through the controller 103, an amplifying section 105 for amplifying video signals of Y, U, V and R, G, B processed through the controller 103 to a level suitable to be displayed, and a switching and deflection section 106 for switching the video signals amplified through the amplifying section 105 and controlling the deflection of a cathode ray tube in horizontal and vertical directions to display the double window pictures.
The controller 103, as shown in FIG. 4, comprises clamp and analog-to-digital (A/D) conversion sections 201 and 301 for clamping and converting the main-channel and sub-channel composite video signals into digital data, respectively, horizontal/vertical filters 202 and 302 for filtering the data converted through the clamp and A/D conversion sections 201 and 301 in horizontal and vertical directions, line memories 203 and 303 for storing the data filtered through the horizontal/vertical filters 202 and 302 line-by-line, phase-locked loop (PLL) and clock generating sections 204 and 304 for controlling the operating timing of the respective circuit blocks, an external memory control section 205 for storing the data provided from the line memories 203 and 303 in an external memory (i.e., the video RAM), reformatting the data stored in the external memory, and storing the reformatted data in a line memory 206 line-by-line, and a display control section 207 for controlling a digital-to-analog (D/A) conversion and buffering section 208 so that the section 208 converts the data from the line memory 206 into an analog video signal, and buffers the converted analog video signal to display the analog video signal on the display screen.
The operation of the conventional ARC apparatus for a doublewindow television receiver as constructed above will now be explained.
Referring to FIG. 1, the sync separating section 10 separates the sync signal from the input luminance signal Y and outputs the separated sync signal to the pulse generating section 20. The pulse generating section 20 generates the pedestal clamping pulse signal utilizing the sync signal.
The luminance detecting section 30 produces a reference voltage in accordance with the pedestal clamping pulse signal outputted from the pulse generating section 20 and detects the existence/nonexistence of the luminance signal by comparing the reference voltage with the luminance signal level during a horizontal scanning period.
The data for the existence/nonexistence of the luminance signal is inputted to the latch 40, and thus the ARC-dedicated microcomputer 50 enters into a rising edge interrupt mode during a vertical sync signal period as shown in FIG. 2. In the rising edge interrupt mode, the ARC-dedicated microcomputer 50 counts the number of the horizontal sync pulses H-sync until the rising edge of the data inputted from the latch 40 is detected in order to detect the point where a horizontal scanning line having the luminance signal starts. At this time, if the luminance signal exists, the data becomes a `high` level, while if the luminance signal does not exist, the data becomes a `low` level.
If the rising edge is detected during the counting operation of the horizontal sync pulses, the currently counted value will correspond to a start point.
If the start point is detected as above, the ARC-dedicated microcomputer 50 resets the currently counted value, enters into a falling edge interrupt mode, and counts the number of the horizontal sync pulses until the falling edge of the data is detected.
If the falling edge is detected during the counting operation of the horizontal sync pulses, the currently counted value will correspond to an end point.
As a result, the interval between the start point and the end point which are detected by counting the horizontal sync pulses will be the width of the horizontal sync signal. The horizontal data regarding the width of the horizontal sync signal is outputted to the main microcomputer 60 to compensate for the deflection data of the deflection circuit.
Meanwhile, the operation of the conventional television receiver having a double window function will now be explained.
Referring to FIG. 3, the main-channel and sub-channel decoders 101 and 102 receive and decode the main-channel and sub-channel composite video signals MCVBS and SCVBS, respectively, and output the decoded signals to the controller 103.
Referring to FIG. 4, the clamp and A/D conversion sections 201 and 202 in the controller 103 clamp the main-channel and sub-channel video signals outputted from the main-channel and sub-channel decoders 101 and 102, and convert the clamped video signals into video data, respectively. The horizontal/vertical filters 202 and 302 filter the converted video data, respectively, and the line memories 203 and 303 store therein the filtered data line-by-line, respectively.
The PLL and clock generating sections 204 and 304 control the operating timing of the respective circuit blocks in the controller 103.
The external memory control section 205 stores the video data in putted from the line memories 203 and 303 in the external memory, reformats the stored data, and stores the reformatted data in the line memory 206 line-by-line.
The display control section 207 controls the D/A conversion and buffering section 208 so that the D/A conversion and buffering section 208 converts the data inputted from the line memory 206 into an analog video signal and buffers the converted analog signal.
The video signals of Y, U, V and R, G, B processed by the controller 103 are amplified through the amplifying section 105 to the level suitable to be displayed, and the amplified video signals are outputted to the switching and deflection section 106. Accordingly, the video signals, the ARs of which are controlled according to the deflection data compensated for by the compensating apparatus of FIG. 1, are displayed on the screen as the double window pictures.
Here, the pixel rate of the video data inputted to the line memories 203 and 303 is determined as follows:
The luminance signal is sampled at a sampling frequency of 1728 horizontal sync pulses (i.e,. about 27 MHz). The sampled luminance signal is filtered through the horizontal/vertical filters 202 and 302, and then down-sampled so as to have a pixel rate of 864 horizontal sync pulses (i.e., about 13.5 MHz).
The size of the picture to be displayed is determined by reducing the video signal through the above-described process. For example, in case of the NTSC type normal picture, the whole picture has 672 pixels per line and has an acquisition area of 228 lines per field. In case of the double window pictures, the picture size is reduced by 1/2 in the horizontal direction, and thus each picture has 336 pixels per line and an acquisition area of 228 lines per field.
There exist various video sources having different ARs such as Cinema of 286 lines (LD), Vista of 324 lines (LD), a 4.times.3 video source of 486 lines, etc. If two video sources having different ARs from each other are inputted to form the double widow pictures, their start and end points where the corresponding video signals start and end during the horizontal sync signal period become different from each other. Accordingly, if the two different video signals inputted to the controller are processed through the clamp and A/D conversion sections and the horizontal/vertical filters, and then stored in the line memories to form the double window pictures, the waveforms of the main-picture and sub-picture signals in the horizontal scanning line, where the main-picture signal exists but no sub-picture signal exists, are represented as shown in FIG. 5, and thus either of the main-picture and the sub-picture displayed on the screen as the double window will leave upper and lower panels (shaded portions) as shown in FIG. 6.
As a result, according to the conventional ARC apparatus as described above, only one video source can be displayed in a full screen, but in a television having a double window function, the AR compensation cannot be respectively effected with respect to two video sources.
Further, even though the picture size can be varied by varying the deflection parameter, such a picture size variation will be simultaneously applicable to both video sources. Accordingly, in case of the two video sources having different ARs, either of the two video sources displayed on the screen will leave unnecessary upper and lower panels as described above.
Furthermore, the vertical size compensation in accordance with the variation of deflection data will bring out the variation of the gap between the horizontal scanning lines, and this exerts a bad influence upon the resolution in the vertical direction.